1. Field of the Invention
This invention relates generally to methods and apparatus for monitoring the displacement of an object so that the distance and rate of movement of the object can be automatically and remotely determined. The invention relates more particularly, but not by way of limitation, to methods and apparatus for determining how far and at what rate a pile is driven.
2. Description of the Prior Art
It is often necessary to monitor an object to determine how far and how fast it moves or is being moved by an outside force. For example, in the construction of offshore petroleum production structures it is necessary to drive piles into the sea floor to support the production platform. To insure that each pile is driven into the proper position to support the portion of the load to be carried by it but is not overdriven to the extent of causing damage to the pile, it is important to know how far and at what rate the pile is being driven. Besides assisting in determining the proper positioning of the pile, this distance and rate information is useful in monitoring the efficiency of the pile driving operation.
Because of the criticality of knowing the distance and rate information of a pile driving operation, there have been attempts at or proposals for various means for compiling this information. For example, white marks have been placed on piles at predetermined intervals, and a person has visually counted and recorded on a manual counting device the number of marks which pass the person (or some other suitable reference point) as the pile is driven. This information can be used to determine the distance the pile has been driven; and with the use of a clock, the rate at which the driving occurs can be determined.
Additionally, high-speed photography has been used to record the motion of the pile as it is being driven. The use of reflected laser light has also been attempted.
Although one may be able to obtain the necessary information from any one of the aforementioned previous attempts or proposals, the previous attempts or proposals may not be suitable for use at night or under high-glare conditions. Additionally, inclement weather can impair the use of the aforementioned techniques. Excessive vibration which can occur in pile-driving operations likewise hampers the use of the foregoing techniques.
Therefore, there is the need for a device which automatically and remotely determines the distance an object has moved and which makes such determinations regardless of the type of weather, time of day or state of the object (e.g., excessive vibration).